1. Field of the Invention
The present invention relates to a method and apparatus for sealing the edges of corrugated plastic material.
2. Description of the Related Art
It has long been known that boxes and containers could be produced from substantially flat sheets of material having fold lines. U.S. Pat. No. 2,102,170, issued Dec. 14, 1937 to Stern, discloses a method and machine for scoring fold lines into paper or cardboard, corrugated or otherwise, to make cardboard or paper boxes. Forming containers from scored plastic sheets is disclosed in U.S. Pat. No. 3,292,513 issued Dec. 20, 1966 to Palmer, and in U.S. Pat. No. 3,495,594. Furthermore, the use of cooperating embossing and flattening rollers is disclosed by Palmer as a means of creating a fold line in plastic sheet materials. More recently, U.S. Pat. No. 4,946,430, issued Aug. 7, 1990 to Kohmann, discloses an apparatus and method for forming at least one shallow fold line (0.15 mm) in thin PVC sheets by first heating the material and then passing the heated material between a pair of rollers. The PVC sheets are heated utilizing heated bars. The fold line is created by the use of a roller which imparts a single substantially "U" shaped groove in the PVC material. See FIG. 11A which shows prior art fold line 31 formed in plastic sheet P utilizing embossing wheel 36 having a single ridge 37.
While the prior art devices are generally adequate for forming thin fold lines plastic materials comprised of plastics with low melting temperatures, the unique problems created by thicker or multilayer higher temperature melting plastic materials render the prior art devices inadequate for forming fold lines in such materials.
For example, the harder plastic materials are generally slippery and tend to slip on the prior art embossing roller systems, which can disrupt system operations and the accurate placement of the fold line. A single groove fold line generally does not provide a structurally sound fold line for thicker or multilayer plastic materials comprised of plastics with higher melting temperatures. In addition the prior art teaches the use of bar heaters which are inadequate for such thicker or multilayer materials. Also, in spite of the prior art teaching that heating only the area to be heat scored will prevent warping, some thicker or multilayer plastics will warp anyway.
Accordingly, there exists a need for an improved heat score machine and method capable of processing harder plastic materials without the slippage experienced by the prior art devices. There also exists a need for an improved machine and method capable of heat scoring thicker or multilayer materials comprised of plastics of higher temperature melting temperatures. In addition, a need exists for an improved fold line pattern that will provide a structurally sound fold line for thicker or multilayer plastic materials.
Corrugated materials, by their very nature, have edges that are "open". Boxes made from such corrugated plastic materials face regulatory hurdles when utilized in applications such as meat handling. Current U.S.D.A. regulations prohibit the use of materials having openings such as those on the side of corrugated materials that will support baterial and viral growth. Thus, there also exists a need for an improved machine and method capable of sealing the edges of plastic corrugated materials.